1. Technical Field
The present invention relates to a virtual image display apparatus which presents a video formed by an image display element or the like to an observer, and particularly relates to a virtual image display apparatus which is appropriate to a head-mounted display which is mounted on the head of the observer.
2. Related Art
Various technologies have been suggested as an optical system which is embedded in a virtual image display apparatus, such as a head-mounted display (hereinafter, referred to as an HMD), which is mounted on the head of an observer (refer to US Patent Application No. 2013-0033756, JP-A-7-333551, JP-A-9-73043, JP-A-2012-58302, JP-A-2005-17775).
In the HMD in the related art, as an apparatus which presents a video to both eyes, a type which blocks external light or a see-trough type which presents a video by using a half mirror as a transparent member and overlapping the external light and video light, is employed (for example, refer to US Patent Application No. 2013-0033756). In the various types of HMD, when the apparatus is used for thoroughly watching a video, it is appropriate to present the image having a long horizontal length in a horizontal direction along the eyes of the observer. Therefore, in most cases, the apparatus presents a horizontally long image.
Meanwhile, as in a case of seeing the presented data while working on something else, the observer does not watch the video thoroughly. When the apparatus is used for so-called watching the video while doing something else, it is desirable to have a small size and a light weight, and an apparatus is known which is designed to be small and light without forming an intermediate image (for example, refer to JP-A-7-333551 and JP-A-9-73043). In addition, since it is necessary to reduce the size and the weight, an apparatus is known which is for one eye, and further, which has a small display portion (for example, refer to JP-A-2012-58302). However, in the one eye type apparatus, for example, there is a possibility that shielding of the front of the eyes due to the video can be reduced when performing some operations while seeing the display of information. However, the size of a display screen is limited by the request for the small size and the light weight, and there is a possibility that the information amount which can be displayed is not sufficient. In addition, even in one eye type apparatus, for example, an apparatus is known which uses a small-sized prism of an aspherical surface and which disposes the video element above the eyes (refer to JP-A-2005-17775), as an optical element which guides the video light to the eyes. In this case, the entire apparatus becomes large, and it is difficult to design the apparatus.